*{
    margin: 0px;
    padding: 0px;
}
/*.bg{*/
    /*width: 100vw;*/
    /*height: 100vh;*/
/*}*/
.bg_canvas{

    display: block;
    margin: 50px auto;
    /*box-sizing: border-box;*/
    box-shadow: -2px -2px 2px #efefef,5px 5px 5px #b9b9b9;
}
.btn{
    width: 150px;
    position: absolute;
    left: calc(50% + 280px);
    top: 50px;
}
.btn_begin{
    width: 100%;
    height: 50px;
    line-height: 50px;
    text-align: center;
    color: #333;
    font-size: 20px;
    background-color: #c1c1c1;
    margin-top: 15px;
}